Suprageneric taxonomy, appeasement behaviour, sex ratio and other aspects of the biology of the myrmecophilous beetle Thorictus grandicollis (Dermestidae, Thorictinae).

1994

Cammaerts R.; Cammaerts M.C.

Following an overview of the literature on the systematic position of the Thoricidae sensu lato, the authors show, on morphological grounds, that they constitute a natural group, considered as the subfamily Thorictinae of the dermestidae. The Thorictinae are divided into two tribes: the Thorictini (comprising the myrmecopnilous genera Thorictus, Macrothorictus and Afrothorictus) and the Thaumaphrastini (comprising the free-living genus Thorictodes). Although larval characters seem to place the Thorictinae closest to the Dermistinae, the morphological organization of the adult differs. Differential diagnoses of the subfamilies and tribes are given as well as comments on the relevance of certain characters. The extent knowledge of the biology of Thorictus foreli Wasmann, the sole Thorictini species which has been studied is summarized. The guest beetle, Thorictus grandicollis Germar, displays characteristic appeasement behaviour when handled by ants. Turning on its back, the beetle immobilizes itself, uncovering its thoracic lateroventral trichomes, allowing them to be investigated and licked by the ants. This particular behaviour and the absence of phoresis on the host's antennae distinguish T. grandicollis from T. foreli. T. grandicollis does not follow its hosts' trail. Its European populations have an extremely female-biased sex-ratio.

Following an overview of the literature on the systematic position of the Thoricidae sensu lato, the authors show, on morphological grounds, that they constitute a natural group, considered as the subfamily Thorictinae of the dermestidae. The Thorictinae are divided into two tribes: the Thorictini (comprising the myrmecopnilous genera Thorictus, Macrothorictus and Afrothorictus) and the Thaumaphrastini (comprising the free-living genus Thorictodes). Although larval characters seem to place the Thorictinae closest to the Dermistinae, the morphological organization of the adult differs. Differential diagnoses of the subfamilies and tribes are given as well as comments on the relevance of certain characters. The extent knowledge of the biology of Thorictus foreli Wasmann, the sole Thorictini species which has been studied is summarized. The guest beetle, Thorictus grandicollis Germar, displays characteristic appeasement behaviour when handled by ants. Turning on its back, the beetle immobilizes itself, uncovering its thoracic lateroventral trichomes, allowing them to be investigated and licked by the ants. This particular behaviour and the absence of phoresis on the host's antennae distinguish T. grandicollis from T. foreli. T. grandicollis does not follow its hosts' trail. Its European populations have an extremely female-biased sex-ratio.